1. Field of the Invention
The present invention relates to a magnetic recording apparatus recording data on a recording medium and, more specifically, to a magnetic recording apparatus using a recording medium allowing high-density recording.
2. Description of the Background Art
Information equipment such as personal computers comes to have remarkably improved functions and, as a result, users are handling ever increasing amount of information. Naturally, there is a strong demand among users for a large capacity storage allowing storage of larger amount of data.
An example of a large capacity storage is a recording apparatus using a hard disk. A hard disk is formed by applying a magnetic substance on a disk-shaped substrate. A hard disk stores information by magnetizing a magnetic layer on the disk surface using a magnetic head.
To realize a storage of larger capacity, the challenge is to improve recording density of a hard disk as the recording medium. In the conventional hard disk described above, in the magnetic layer formed uniformly and continuously on the medium surface, a recording mark as a unit of data writing has a serrated edge. The serrated shape causes noise (transition noise) at the time of reproduction, which noise lowers S/N ratio (Signal to Noise Ratio), leading to a problem that the recorded information cannot be correctly reproduced.
In order to improve recording density, it is also necessary to reduce the size of recording mark itself. In a conventional hard disk, recording marks are formed on a uniformly formed magnetic layer and, therefore, when the marks are made smaller to increase density, magnetism interference occurs between recording marks. As a result, correct recording of information becomes difficult, or correct reproduction of recorded information becomes difficult.
A solution to such problems is “patterned medium.” The patterned medium refers to a magnetic recording medium having an array of magnetically isolated magnetic recording cells. The magnetic recording cell consists of particles of magnetic material arranged regularly at a constant interval in a non-magnetic material. The magnetic recording cell stores a piece of magnetic information, and the edge of recording mark is the edge of magnetic recording cell. As a result, when patterned medium is used as the recording medium, the noise at the time of reproduction and the magnetic interference between recording marks can be reduced, whereby the recording density can significantly be improved.
In the patterned medium, magnetic field is generated in accordance with the magnetic recording cells formed in advance, to record information. Therefore, it is necessary to adjust timings and to generate electric field with high accuracy with respect to the magnetic recording cells.
Japanese Patent Laying-Open No. 2003-281701 (hereinafter referred to as “'701 Reference”) discloses a magnetic recording medium using patterned medium, in which the timing for generating magnetic field is adjusted by detecting leakage magnetic field at the time of recording. According to the technique disclosed in '701 Reference, utilizing the fact that the leakage magnetic field when a magnetic writing element is on a magnetic recording cell of the media is different from the leakage magnetic field when the element is not on the magnetic recording portion, the timing is adjusted such that the magnetic writing element generates magnetic field on a magnetic recording cell on the media.
The pitch between magnetic recording cells formed on a high-density magnetic recording medium such as the patterned medium is as narrow as several nm. Therefore, even a slight deviation between the position of magnetic writing element of a recording/reproducing head for recording and the position of a desired magnetic recording cell easily leads to a recording error. Therefore, generation of electric field at the optimal timing is essential in the magnetic recording apparatus using patterned medium.
When the magnetic recording apparatus controls positioning of the magnetic writing element with respect to the magnetic recording medium, typically required positioning accuracy of the magnetic writing element in the circumferential direction of magnetic recording medium is at most 10% of the pitch between magnetic recording cells, that is, at most a few nm. Considering the surface recording density of about 1 terra byte (Tb)/in2, the accuracy of about 1 nm is required. Since the magnetic recording medium moves relative to the magnetic writing element, positioning control of the magnetic writing element equivalently means timing control of magnetic field generation. If the linear velocity to the circumferential direction of magnetic recording medium is several m/s, timing control of about several ps is required.
According to the technique of '701 Reference, the magnetic field detecting element detects, together with the leakage magnetic field from the magnetic field generating element, the magnetic field recorded on the medium. Therefore, it has been necessary to separate a signal for timing adjustment. Depending on the distance between the magnetic field generating element and the magnetic field detecting element, a peak of magnetic signal from the medium and a peak of leakage magnetic field signal may be detected substantially at the same time, making signal separation difficult. Further, the leakage magnetic field signal tends to be smaller than a signal from the medium and, therefore, detection error may possibly be caused by only a slight noise at the time of detection. Further, variation among individual media makes it difficult to uniformly control timings.